DORASAN OBSERVATION POST, South Korea — A convoy of 15 South Korean dump trucks rumbled across the heavily fortified border Friday, returning home with North Korean sand in a symbolic trip that raised hopes for breaching a Cold War frontier for the sake of trade.

North Korea has been extremely reluctant to open its land border with South Korea. The Koreas remains divided following the 1950-53 Korean War, which ended in a cease-fire, not a peace treaty. Their border is guarded by barbed wires, battle-ready military units, and mine fields.

Friday's truckloads were yet another sign of North Korea's willingness to open its border with South Korea for commercial profits. South Korean tourists are already crossing the eastern border to visit the North's scenic Diamond Mountain.

South Korea, suffering a shortage of construction materials, has imported over 33,000 tons of North Korean sand since 2002. But until Friday, all the law material shipments from North Korea came through China or by ship.

Sanctioned tradeAfter a historic 2000 inter-Korean summit, South Korea began sanctioning trade with North Korea, which badly need trade and investment from the outside to help rebuild its shattered economy.

Last month, North Korea allowed South Korean trucks to cross the border to deliver relief goods for the victims of a deadly train explosion in the impoverished North.

Friday's trucks were hired by a South Korean construction company that has recently signed a deal to import 1,000 tons of sand from a North Korean river near the border. The cross-border transport will continue through Sunday. No further details of the deal were immediately available.

Following the 2000 summit, inter-Korean trade picked up the pace. The South's imports totaled $61.59 million in the January-March period. Shipments to the North amounted to $42.7 million.

Last year, inter-Korean trade totaled $724 million, up from $641 million in 2002. South Korea imports fisheries products and raw materials from the North. It exports textiles and steel products.

South Korea is building an industrial complex in Kaesong, a North Korean town just north of the border. Beginning late this year, it will host South Korean companies hoping to capitalize on cheap North Korean labor, while their operation will provide the North with badly needed cash.